Court documents show Pena told investigators that back in November, she returned home after being incarcerated, to find her son lying on a bed wrapped in a blanket and noticed that "his body was stiff and he was not showing any signs of life."

Pena said she went outside to confront Ferguson on what happened and says he went inside and removed the boy's "lifeless body" from the room, placed him in a car and drove away. Pena told investigators she never talked to Ferguson about what happend because she was scared to ask and that he "had an extensive history of violence and being physically abusive."

She told deputies Ferguson later drove her to an area off State Road 503, where Ferguson claimed he buried Jeremiah. That allegedly took place on Dec. 6 -- Valencia's birthday.

Deputies were tipped off to investigate the death on the afternoon on Jan. 25 after an inmate contacted them about a possible homicide. According to the affidavit, while incarcerated, Pena told the inmate about the death of her child and said her boyfriend was responsible.

The next day, investigators learned Pena's family had concerns about the safety of Pena's children. An aunt and a step-sister told deputies the last time they heard from the 13-year-old was in July 2017.

Deputies then began to conduct interviews with Pena, Ferguson and Nunez, who is Ferguson's biological son.

The report states that after initially lying to investigators about what happened, Nunez said Valencia did something to anger Ferguson, and that's when Ferguson punched the 13-year-old in the face and stomach several times. Nunez then told deputies that Ferguson dragged the teen into a room and locked the door.

When questioned by investigators, Ferguson said Valencia was injured during some aggressive play with a sibling and he did not call law enforcement "because he would be accused of being involved in Jeremiah's death," the affidavit states.

Nunez also told deputies that Ferguson has a history of abuse. Ferguson's previous criminal history includes kidnapping, aggravated assault and battery, child abuse and criminal sexual penetration. Pena's criminal history includes property crimes and drug possession.

"I am sickened by this horrific tragedy," First Judicial District Attorney Marco Serna said in a statement Monday night. "We are a close-knit community and this touches so many of our families."

Serna, Santa Fe County Sheriff Robert Garcia and New Mexico State Police Chief Pete Kassetas will hold a joint press conference Tuesday at 11 a.m., where more information is expected to be released.

"I want northern New Mexicans to know this case is of the highest priority and I will do everything in my power to seek justice for this innocent child," Serna said. "We are in the very early stages of this tragedy, so tonight I ask all of New Mexico to pray for our community."